Curb frames for skylight constructions are known, attention being invited for example to Jentoft et al, U.S. Pat. No. Re 32,915, the contents of which are hereby incorporated by reference. The Jentoft et al curb frame includes an outside edge gasket 50, 150 integrally formed with the curb frame but of flexible co-extruded PVC having a durometer A hardness of 72.+-.3, i.e. soft vinyl wherein the remainder of the curb frame, with the exception of another co-extruded gasket portion, is formed of rigid vinyl having a durometer D hardness of 82.+-.3.
A disadvantage of this construction lies in its critical dual durometer construction requiring a 3-section extruder and die which necessitate a substantial capital investment. Dual durometer co-extrusion is also more difficult than single durometer extrusion in that it is more susceptible to the production of unsatisfactory product which must be scraped when inevitable variations occur during the extrusion process. As a result, the curb frame of Jentoft et al U.S. Pat. No. Re 32,915 is more expensive than desirable.
Jentoft et al U.S. Pat. No. 4,862,657 shows a different construction of a curb frame, here referred to as an operating leaf frame or support frame 20, this curb frame having no outside edge gasket whatsoever. In this construction, the curb frame is supported by an inwardly extending flange 38 from the retainer 22. Sealing in this case is accomplished between the retainer 22 and the base frame 14. This construction, particularly adapted for a ventilating skylight, i.e. one which is capable of opening, is considerably more complex and hence more costly than that of the previously mentioned Jentoft et al U.S. Pat. No. Re 32,915.